1. Field of the Invention
The present invention relates to a tray of an optical disk player, and in particular to a tray of an optical disk player capable of preventing flutter having a bad influence upon recording and reproducing in high speed rotation.
2. Description of the Related Art
Recently, researches on developing an optical disk player having an operational speed not less than 10000 rpm and a fifty-two times speed have been proceeded, recording/reproducing speed of other disks of a CD group or a DVD group have been improved continually. Accordingly, several mechanical problems related to the high-times speed trend of the optical disk reproducing apparatus have been occurred, and a countermeasure for them have been required.
When a disk is rotated in the air, the disk may vibrate by variable mass unbalance or the air.
When a rotational speed is not greater than a specific speed, because an air flow may act as an irregular excitation source, resonance may occur not by the air but by variable mass unbalance of the disk. However, when a rotational speed is riot less than a specific speed, because a disk is strongly coupled to the air, although variable mass unbalance does not exist, severe unbalance may occur in frequencies regardless of the rotational speed. Herein, vibration of the disk coupled to the air is called flutter, and the specific speed is called a flutter speed.
In the operation of the disk player, the flutter makes a head or a pickup of the disk player not follow a signal track on the disk accurately in reproducing/recording, and accordingly incorrect information may be reproduced/recorded.
Scientific researches on the flutter have been performed in relation to a hard disk. A method for attenuating flutter phenomenon by changing a channel and improving a structure of a hard disk was disclosed in Korea Patent No. 2001-0053127 and Korea Patent No. 2001-0064503. In addition, a method for preventing flutter by increasing strength of an optical disk by fabricating the optical disk by a specific fabrication method and generating residual stress inside a disk medium was disclosed in Korea Patent No. 1999-0001808.
However, in case of a hard disk, flutter can be prevented in advance in the early stage of production by fabricating a disk and an enclosure precisely. However, in case of an optical disk, because of floods of manufacturers, inferior disks in which modulus of elasticity is remarkably low and thickness thereof is thin are circulated in the market, and accordingly flutter may occur at a low rotational speed. Accordingly, an optical disk player has to be capable of preventing flutter in a random disk.
FIG. 1 is a perspective view illustrating an optical disk player in accordance with the conventional art.
The conventional optical disk player includes a tray main body 11 consisting of the tray front end 11a, the tray rear end 11b and the top tray 11c; a large-sized disk mounting portion 20 depressed on the top tray 11c centering around the center of a spindle 25 as a concentric circle; a small-sized disk mounting portion 23 depressed on the large-sized disk mounting portion 20; and a spindle opening 24 pierced-formed on the tray top surface 11c so that a optical pick-up (not shown) can approach to the disk.
A front wall 21 is formed on the front of the large-sized disk mounting portion 20, and a rear wall 22 is formed on the rear of the large-sized disk mounting portion 20.
FIG. 2 is a schematic plane-view illustrating the tray of the optical disk player on which a large-sized disk is mounted.
In order to prevent collision of the tray main body 11 and the outer circumference of the disk 15 when the mounted disk 15 is rotated, the large-sized mounting portion 20 is formed so as to be greater than the disk 15.
In addition, it is general to have a gap of 1.75 mm between the front wall 21 of the large-sized mounting portion 20 and the disk 15.
FIG. 3 is a graph showing measuring results of a disk's rotational speed to axial displacement in the operation of the tray in FIG. 1.
In FIG. 3, a horizontal axis is a disk's rotational speed (Hz), and a vertical axis is z-axial displacement (hereinafter referred to as ‘axial displacement).
In the results, because a disk having small variable mass unbalance is used, significant vibration does not occur in a range before flutter occurrence. However, approximately over 160 Hz, vibration of the disk generates displacement much greater than general resonance, the vibration has a bad influence upon reproducing/recording of the disk. The rotational speed of 160 Hz is much lower that the speed of the fifty-two times driver of which speed is 173 Hz. Thus the flutter occurring at the speed of 160 Hz may cause wrong operation, damage the disk and endanger user safety, when the above-described tray is used in fifty-two times driver.